Optical amplifiers, especially erbium doped fiber amplifiers (EDFAs), are largely used in the optical communication systems for increasing the signal transmission distance. It is well known that optical amplifiers, fiber or semiconductor based, with or without the presence of an input signal, emit a fluorescent light called Amplified Spontaneous Emission (ASE). This ASE is of low temporal coherence, and emits within a wide wavelength range.
In the case of an erbium doped fiber amplifier, ASE has a peak around 1530 nm, then the power density decreases, having a dip around 1542 nm, increases slightly again and reaches a plateau centered around 1550 nm. The spectrum has a 3-dB bandwidth of about 9 nm. The density difference between the peak at 1530 nm and the plateau around 1550 nm is about 15 dB. The spectrum is not flat.
A much wider 3-dB bandwidth and a flat spectrum output would be of great use for passive component testing, spectroscopy, fiber sensor, fiber gyroscopes, optical coherence tomography etc., for replacement of existing tunable lasers, for much lower cost and for much faster and easier testing results, especially for passive component manufacturers. Combined with a scanning filter, it would be able to provide a true continuously tunable light source without any frequency steps, which is critical for material structure analysis. However, the existing narrow 3 dB bandwidth is not sufficient for these applications.